Iron is one of the most abundant mineral on earth and is essential to normal human physiology.  About 2/3 of the body’s iron is found in hemoglobin, the protein in red blood cells that carries oxygen to cells.  An adequate supply of iron is necessary for the body to produce hemoglobin and red blood cells.  If too little iron is available, fewer and/or smaller RBC’s are produced, leading to decreased oxygen carrying capacity of the blood.  This is called iron deficiency anemia and can cause fatigue, poor work capacity, and decreased immunity. 


Endurance athletes depend on efficient oxygen delivery to working muscles, so even mild anemia can have deleterious effects on performance.  Some hypothesize that iron deficiency, even without anemia, can impair endurance.  However, one review showed that in seven of 8 studies that although iron supplementation does increase iron stores, as measured by ferritin levels, no increase in performance was found unless hemoglobin also increased. In the eighth study, there was an unexplainable drop in endurance performance in the control group which confounded the results. (Garza 1997)


Dietary iron comes in two forms:  heme and non-heme.  Heme iron is found in animal foods that originally contained hemoglobin, such as meat, fish, and poultry.  Non-heme iron comes in foods such as beans, spinach, raisins, and fortified cereals and breads.  Heme iron is better absorbed than non-hem iron, but most dietary iron is non-heme.  The recommended daily value for iron intake is 18 milligrams of elemental iron.  Three ounces of beef contains 3.2 mg of heme iron and one cup of lima beans contains 4.5 mg of non-heme iron.  Absorption of non-heme iron can be increased by consuming it with heme iron or with ascorbic acid (vitamin C).  Some substances that decrease iron absorption are the tannins and polyphenols found in tea and coffee, calcium, and phytates found in whole grains and legumes.  One study showed that taking 30-50 mg of ascorbic acid can overcome the inhibitory effects of tannins and phytate on iron absorption.  (Siegenberg 1991)


There is contradictory evidence on the prevalence of iron deficiency anemia in athletes.  Most studies show an increased prevalence of iron deficiency anemia in athletes.  One study showed that iron deficiency developed over an 11 week cross country season, with 17% of males and 45% of females becoming iron deficient.(Rowland 1987) Dietary choices may explain most of  this, but evidence exists for increased iron and red blood cell turnover. (Beard 2000)  Intense exercise may increase the need for iron by 30%.  This may be due to increase red blood cell turnover, effects of increased nitric oxide or other unknown mechanisms.   In sports, especially in endurance sports where low body weight can be an advantage, caloric restriction can result in inadequate dietary iron intake. Females, especially those with heavy menstrual periods or with eating disorders, are especially prone to iron deficiency.  However, the most common cause of a low hematocrit (a ratio of red blood cells to whole blood) in athletes is pseudo-anemia, which is a dilution of the blood caused by plasma expansion.  This is not true anemia, as the actual number of red blood cells is not decreased. (Portal 2003) Another study showed that endurance athletes were less likely than the general population to have iron deficiency.  Out of 52 controls, 50% were iron deficient, and out of 126 atheletes, 26% were iron deficient.  (Malczewska 2000)


Iron supplementation is indicated when an athlete has iron deficiency anemia and dietary sources are not sufficient to replace the necessary iron.  A low iron level with a low normal hemoglobin may be a relative indication for iron supplementation in order to increase performance.  Iron supplementation is available in ferrous and ferric forms, with ferrous forms being the best absorbed.  Ferrous fumarate contains 33% elemental iron, ferrous sulfate contains 20%, and ferrous gluconate contains 12%.  Therapeutic doses of iron supplements may cause side effects such as nausea, vomiting, constipation, diarrhea, dark colored stools and/or abdominal distress.  Taking the supplement in two or three divided doses and with food and titrating up to the recommended dose may help limit these symptoms.  Rarely, iron injections are needed, but require close medical supervision. 


Should all athletes supplement with iron?  The answer is no.  Anemia has many causes.  It can be due to decreased production of red blood cells, blood loss, or increased destruction, such as heel-strike hemolysis in runners.  Decreased production can be due to bone marrow abnormalities, kidney problems, or more commonly, nutritional deficiencies.  Vitamin B12 and folate deficiencies can also cause anemia.  A physician can determine the presence or absence of anemia and do testing to determine the cause and direct appropriate treatment.   Iron overload can occur with excessive supplementation or in people with genetic diseases such as hereditary hemochromatosis.  Hemachromatosis affects one in 250 individuals of northern European descent and causes extremely efficient absorption and storage of iron.  The iron is stored in body organs, resulting in cirrhosis of the liver, heart failure, possibly cancer.(Fauci 1998)  Indiscriminate iron supplementation may induce hemochromatosis in susceptible individuals.(Zoller, 2004)   High iron stores have also been linked to ischemic heart disease.  Some have suggested a protective effect of iron depletion on cardiovascular disease.(Sullivan 2007)


Of particular concern is athletes taking iron in the hopes of increasing their performance and developing iron overload, eventually experiencing the above complications.  In 1999, the Union Cycliste Internationale (UCI) began systematically testing athletes in the wake of the doping scandals uncovered in the 1998 Tour de France.  Four times a year, all professional cyclists were required to submit to a battery of blood tests.  The most glaring abnormality found in these tests was a high ferritin level, indicating high iron stores.  The upper normal limit of ferritin is 300 ng/ml, and the average ferritin value in the 1000-plus athletes tested was 342 ng/ml.  Almost half the cyclists had ferritin levels over 300 ng/ml, and one fourth had levels over 500 ng/ml.  Iron supplementation has long been practiced by cyclists in the belief that iron enhances performance by increasing red blood cells.  This actually is true only in iron deficiency anemia.  Two concerns were raised:  First, high levels of iron storage cause organ damage and the high levels persisted even after supplementation ceased.  Second, excessive iron supplementation is linked with blood doping.  The use of EPO to boost red blood cell production increases the body’s need for iron.  The good news is that average ferritin values have decreased by 33% between 1999 and 2002.(Deugnier 2002, Zotter 2004)


Iron deficiency can occur in non-anemic individuals as well.  This condition is marked by normal hematocrit, normal hemoglobin, decreased serum  ferritin, and corresponding increased serum transferrin receptor.  Iron supplementation with 30 mg of elemental iron daily as Ferrous Sulfate for six weeks in a group of non-anemic, iron deficient athletes has been shown to correct iron deficiency, without increasing hematocrit beyond normal ranges.  Why is this important for athletes?  In that same iron deficient, non-anemic population, the iron supplement group demonstrated  an significant increase in ventilatory threshold, energetic efficiency, and progressive fatigue resistance, when compared to placebo.  (Hinton 2007, Brownlie 2004, Brutsaert 2003)


In summary, iron deficiency anemia decreases endurance performance and intense exercise may increase iron requirements.  Some groups of athletes, particularly menstruating female and vegetarian athletes, distance runners, and those on caloric restricted diets, are more prone to iron deficiency anemia.  Iron supplementation is common in endurance sports, and will help endurance performance in anemia caused by iron deficiency. However, because anemia can have many different causes, a low hemoglobin, especially if not responsive to iron supplementation, needs a complete medical workup. When iron supplementation is indicated, hemoglobin and ferritin levels should be checked regularly, to prevent complications from iron overload. 




Beard J, Tobin B.  Iron status and exercise.  Am J Clin Nutr.  2000; 72(2 Suppl):594S-7S.


Brownlie T 4th, Utermohlen V, Hinton PS, Haas JD. Tissue iron deficiency without anemia impairs adaptation in endurance capacity after aerobic training in previously untrained women.   Am J Clin Nutr. 2004 Mar;79(3):437-43.


Brutsaert TD, Hernandez-Cordero S, Rivera J, Viola T, Hughes G, Haas JD. Iron supplementation improves progressive fatigue resistance during dynamic knee extensor exercise in iron-depleted, nonanemic women.   Am J Clin Nutr. 2003 Feb;77(2):441-8.


Deugnier Y, Loreal O, Carre F, Zoulim F, Vinel JP, Paris JC, Blaison D, Moirand R, Turlin B, Gandon Y, David V, Megret A, Guinot M.   Increased body iron stores in elite road cyclists.  Med Sci Sports Exerc.  2002 May; 34(5):876-80.


Fallon KE.  Utility of hematological and iron-related screening in elite athletes.  Clin J Sport Med. 2004 May;14(3):145-52.


Fauci AS, Braunwald E, Isselbacher KJ, Wilson JD, Martin JB, Kasper DL, Hauser SL, Longo DL.  Harrison’s Principles of Internal Medicine Companion Handbook.  1998:980-1.


Garza D, Shrier I, Kohl HW 3rd, Ford P, Brown M, Matheson GO.  The clinical value of serum ferritin tests in endurance athletes.  Clin J Sport Med. 1997 Jan;7(1):46-53.


Hinton PS, Sinclair LM. Iron supplementation maintains ventilatory threshold and improves energetic efficiency in iron-deficient nonanemic athletes. Eur J Clin Nutr. 2007 Jan;61(1):30-9. Epub 2006 Jul 12.


Malczewska J, Raczynski G, Stupnicki R.  Iron status in femal endurance athletes and in non-athletes.  Int J Sport Nutr Exerc Metab.  2000 Sep; 10(3):260-276.


Office of Dietary Supplements. National Institutes of Health.  Dietary Supplement Fact Sheet:  Iron.  2004.


Portal S, Epstein M Dubnov G.  Iron deficiency and anemia in female athletes–causes and risks.  Harefuah.  2003; 142(10):698-703, 717.


Rodenberg RE, Gustafson S.  Iron as an ergogenic aid:  ironclad evidence?  Curr Sports Med Rep. 2007 Jul;6(4):258-64.


Rowland TW, Black SA, Kelleher JF.  Iron deficiency in adolescent endurance athletes.  J Adolesc Health Care.  1987 Jul;8(4):322-6.


Siegenberg D, Baynes RD, Bothwell TH, Macfarlane BJ, Lamparelli RD, Car Ng, MacPhail P, Schmidt U, Tal A, Mayet F.  Ascorbic acid prevents the dose-dependent inhibitory effects of polyphenols and phytates on nonheme-iron absorption.  Am J Clin Nutr.  1991 Feb;53(2):537-41.


Suedekum NA, Dimeff RJ.  Iron and the athlete.  Curr Sports Med Rep.  2005; 4(4):199-202.


Sullivan JL, Mascitelli L.  Current status of the iron hypothesis of cardiovascular diseases.  Recenti Prog Med.  2007 Jul-Aug;98(7-8):373-7.


The Merck Manual of Health & Aging.  Anemia.


Zoller H, Vogel W.  Iron supplementation in athletes–first do no harm.  Nutrition. 2004 Jul-Aug;20(7-8):615-9.


Zotter H, Robinson N, Zorzoli M, Schattenberg L, Saugy M, Mangin P.  Abnormally high ferritin levels among professional road cyclists.  Br J Sports Med.  2004 Dec: 38(6):704-8.




  1. Cindy O'Reilly says:

    I started researching 1st Endurance because I found your last report on Iron and Endurance Athletes. That was a great report! I have been dealing with iron deficiency anaemia for almost one full year. It has not been an easy year. Training is very challenging. I discovered that your MultiV had Ferrochell in it. That was like discovering gold! I looked further into the products that 1st Endurance has to offer and was impressed with what I found. I started using MultiV and noticed my anaemia was having a positive reaction to the combination of products immediately. I am now recovering better as well. Even my labs show that my Ferritin is going up. I am very pleased. I just had a PR in my last race!
    My concentration, energy and regular abilities to swim, bike, run, do yoga, walk, and just breathe are so much better now.
    Thank you 1st Endurance!

  2. Robert Kunz says:

    Thank you for your comments on Iron and what you have experienced with MultiV. Low Ferritin levels seems to be more prevalent than the research suggests. We get many customers who start taking MultiV and immediately feel renewed energy which is likely driven by improvements in their Ferritin levels. Two members on our Endurance Research Board have both experienced these improvements, with one (Bob Seebohar) measuring significant increases in his Ferritin after only a couple weeks.

  3. Jeffrey Rocco says:

    I agree. Personally, I believe that the iron in MultiV has made a significant difference. I believe that I did have iron deficiency without anemia. Since using MultiV, I have experienced better energy levels for better training and racing. My wife has had a similar experience. As an example, last week at the Xterra Mountain regional championships, I improved my time 23 minutes over last year’s performance (on the same course). I took second place in the sport Clydesdale division. I had very good energy levels during the race, and at the end I felt very good–not depleted, and ready to go again.

  4. Bob Seebohar says:

    I thought I would let you in on a little experiment I did with myself.

    I stopped taking the MultiV for 2 months and then had blood work done to test my ferritin levels (12/07). I then started taking MultiV (3 tabs per day) for 2 months and had my ferritin measured again (2/08). My initial ferritin reading was 49 and two months later it was 79!

    The only factor that may have influenced this result on a small level was the fact that I was not training much the two weeks leading up to my second blood test due to being very sick.

    However, even given that, this is a tremendous finding and support of the use of the MultiV, even though it was only an n of 1. My daily diet was very similar to what I normally do (I don’t stray too far from my norm) and I am a vegetarian.

  5. David says:

    This is a fascinating article that relates to my training, but because of some of the subtleties and technicalities, I am not sure whether I need to take action. I have been training for half ironman events for 2 years. During several events, I had severe leg cramping during the run, so began to investigate potential causes. Although I am a heavy sweater, my coach and I thought that issue had been addressed through sports drinks and electrolyte replacement. To investigate more deeply, we examined a blood test taken in season, and also created a recent baseline test out of season. I am not suggesting that the iron levels have anything to do with the cramping, but that perhaps another issue exists which needs to be addressed. Because of the various measurements (iron, TIBC, transferrin saturation), it is unclear whether my iron levels would be considered “very low” and if so, what kind of supplement should be taken to remedy. Here are my baseline results:
    Iron: 64 mcg/dl
    TIBC: 309 mcg/dl
    Transferring saturation: 21%
    Ferritin: 129 ng/ml
    The doctor thinks these levels are fine, but it is not clear he is taking into account my endurance training.

  6. Jeff Rocco says:

    Response to David’s Question:
    David ,

    Your Iron numbers look ok at first glance. The primary indicator for non-anemic iron deficiency is serum ferritin with a normal range of 10-200ng/ml. Yours is within that normal range. However, in the studies above, Brutsaert defined iron deficient as Ferritin<20mcg/L (equal to 200ng/ml), and Hinton defined iron deficient as Ferritin<16mcg/L. According to those definitions, you may be considered Iron deficient. In the studies by Brutsaert and Hinton, there was a significant improvement in muscular fatigue resistance and ventilatory threshold for athletes with ferritin levels in your range. Another clue to modestly low iron stores is your Total Iron Binding Capacity (TIBC) at the upper end of the normal range (“normal”=250-375 mcg/dl). A higher TIBC means that the body is “looking for iron” and looking to incorporate iron into bone marrow reticulocytes (immature red blood cells).

    Looking at Bob Seebohar’s and my own personal experiences above, I believe that you could most likely benefit from Iron supplementation. The chelated Iron source in Multi-V is very well absorbed, and should be enough to top off your body’s iron stores.

    Back to considering your cramps for a moment… Calcium and Magnesium are critical electrolytes for muscle function, and deficiencies can be responsible for cramping. Consider your electrolyte replacement beverage. Does it contain adequate Calcium and Magnesium? See

    MultiV contains Magnesium. EFS drink, bars, and liquid shot all contain significant levels of Calcium and Magnesium. Ultragen also has significant levels of Calcium and Magnesium.

    Good Luck in your training, and let us know how you are doing in 6-8 weeks.

  7. Emma Harley says:

    This is very informative and goes some way to explaining my situation really being a marathon runner. What amazed me is why no-one picked up on the lack of iron and only did so after i’d been ‘drained’ through exercise. I too am supplementing with iron and my levels have come back up but now I have the added side effect of constipation, so i’ve adjusted my doses (as recommended by my nutritionist) and hopefully this will help to correct this.


  8. Emma,
    Consider using a source like Iron Amino Acid Chelate found in our MultiV and you may find the constipation to subside.

  9. Force Factor says:

    well,this is awesome post. i have red your post. it was pretty good you have made some good points. thanks for sharing

  10. Edie Bogdanski says:

    I was looking for more personal opinions on this issue today when I came upon your really interesting blog post…thanks a million for sharing. I will surely be checking up on your blog and visiting again to read new articles.BTW since when have you been blogging? :)

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